lnwallet/test_utils: make CreateTestChannel return random funding op

Previously it would always be the same, resulting in multiple calls to
the method not being usabel to create more than one set of channels.

lnwallet/test_utils.go

@@ -7,6 +7,7 @@ import (
 	"encoding/hex"
 	"io"
 	"io/ioutil"
+	prand "math/rand"
 	"net"
 	"os"
 
@@ -102,7 +103,7 @@ func CreateTestChannels() (*LightningChannel, *LightningChannel, func(), error)
 
 	prevOut := &wire.OutPoint{
 		Hash:  chainhash.Hash(testHdSeed),
-		Index: 0,
+		Index: prand.Uint32(),
 	}
 	fundingTxIn := wire.NewTxIn(prevOut, nil, nil)